Our previous studies indicate that species-specific cell recognition in cellular slime molds is mediated by high affinity interactions of cell surface carbohydrate-binding proteins (lectins) with complementary oligosaccharide-containing receptors. The proposed research would continue these studies in slime molds, combining biochemical, cell biological, and morphological techniques to investigate four major problems: 1) The isolation and physical characterization of the cell surface receptors for the lectins; comparison of receptors from different species to determine functionally-relevant structural differences; 2) binding measurements of lectins to homotypic and heterotypic slime mold cells; correlation with direct measurements of cell-to-cell binding between homotypic and heterotypic cells, in order to further evaluate the role of lectins and receptors in species-specific cell recognition; 3) regulation and processing of cell surface lectins and their receptors: sites of synthesis, routes of intracellular transport to the cell surface, mechanism of regulation of cell surface receptor; 4) role of cell surface lectin-receptor interactions in the induction of enzyme programs within developing amoebae. In addition, the proposed research would apply the theoretical frame-work and methodologies developed in the slime mold work to the study of the recently discovered endogenous lectins in fibroblasts. The potential role of these lectins (or others that might be identified) in the cellular interactions of normal and oncogenically-transformed fibroblasts will be evaluated. These studies should add to our understanding of fundamental mechanisms of cell interactions, which is a central problem in cell biology today.